On Tue, 23 Jul 2019 at 19:21, Tom Lane <t...@sss.pgh.pa.us> wrote: > > Martijn van Oosterhout <klep...@gmail.com> writes: > > 2. Add a field to AsyncQueueEntry which points to the next listening > > backend. This would allow the loops over all listening backends to > > complete much faster, especially in the normal case where there are > > not many listeners relative to the number of backends. The downside is > > this requires an exclusive lock to remove listeners, but that doesn't > > seem a big problem. > > I don't understand how that would work? The sending backend doesn't > know what the "next listening backend" is. Having to scan the whole > queue when a listener unlistens seems pretty awful too, especially > if you need exclusive lock while doing so.
I mean tracking the listening backends specifically, so you can replace the loops: for (i=0; i < MaxBackends; i++) with for (i=QUEUE_FIRST_LISTENING_BACKEND; i; i = QUEUE_NEXT_LISTENING_BACKEND(i)) Such loops occur often when trying to advance the tail, when adding a new listener, when sending a notify, etc, all while holding a (exclusive) lock. Seems like such an easy win to only loop over the listening backends rather than all of them. > > Do 2 & 3 seem like a good direction to go? I can probably work something up. > > I'm on board with 3, obviously. Not following what you have in mind > for 2. Hope this clears it up a bit. Only waking up one at a time is a good idea, but needs to some careful thinking to prove it actually works. Have a nice day, -- Martijn van Oosterhout <klep...@gmail.com> http://svana.org/kleptog/
